1. Field of the Invention
The present invention relates generally to injection molding systems and ejection subsystems for use therein and, in particular, to adjustable knockout rods to effect the proper ejection of articles of manufacture made by injection molding systems.
2. Discussion of the Background
In general, the art of injection molding is well known. A mold, usually comprised of two parts having matching spaced apart surfaces to form a cavity for receiving injection material, forms the major component of the injection molding machine. Usually, one of the mold parts is movable relative to the other to facilitate removal of the article of manufacture which is formed within the mold. The movable mold is provided with an ejector for removing the article of manufacture from the mold surface.
Currently, a conventional knockout is an iron cylinder bar of approximately one inch in diameter and a length that fluctuates between approximately 8 and 14 inches. It has screw thread in both sides that varies between ½″ and ⅝″. This is used to support the ejector plate of the mold in the machine's piston to realize its function: remove the unit already fabricated in the mold and return it to its original position. Every knockout mold has its own specification.
U.S. Pat. No. 3,448,488 to Kiraly discloses a “quick adjustment knockout rod”, but not an adjustable one, where adjustable ejector actuating means are provided to actuate the ejector at a certain position of travel of the movable mold. Prior to Kiraly ejector actuating means of the prior art had been of the threaded bar type which are threadedly secured to a stationary portion of the injection molding machine. Thus, when the molds of the injection molding machine are changed to manufacture different articles, it is often necessary to also change the position of the threaded bar to insure that the ejector is actuated properly. This bar, or knockout rod, must be unfastened from its locked position and threadedly adjusted to vary its length and then again locked in place. It is common to utilize two or more knockout rods to effect proper ejection of an article of manufacture. Therefore, each knockout rod must be accurately adjusted so as to work together.
In so adjusting the position of the knockout rods of the prior art, prior to the Kiraly invention, a time interval of approximately 45 minutes was required to adjust the length of the rod over a distance of 30 inches.
Therefore, one of the primary objects of the Kiraly invention, particularly from a maintaining standpoint, was to provide a knockout rod for injection molding machines which could be adjusted accurately over short and long lengths in a minimum of time.
Another object was to provide a knockout rod for injection molding machines which had a finite number of adjustable positions and an infinite number of adjustable positions in between each finite position.
An injection molding machine operates so rapidly that it can quickly finish a run of a particular molded part in a comparatively short period of time. In view of the substantial cost of the machine, it cannot be allowed to sit idle. The mold base in the machine has to be removed and a new mold base inserted so that the machine can continue to operate. The time taken in changing the mold base must be limited so the machine can begin productive use. It currently takes from one to several hours to complete a mold base change. This lost time has a marked effect on the profitability of a company.
In order to speed up the mold change process, attempts have been made to equip the platens of the molding machine with an array of clamps and guides for supporting the mold base.
The problem of changing mold bases is not limited to injection molding machines. Similar problems are presented in changing the die or mold in a stamping press. In both situations, the mold set weighs a substantial amount and must be handled carefully to avoid damage to the mold, die, and press.
At the present time, there does not appear to be a simple system for interchanging mold bases in less than one hour. Also, there does not appear to be a simple system that would allow many different size mold bases to be equipped with a common ear plate which would enable the mold bases to be readily changed in a molding process. U.S. Pat. No. 5,439,368 to Martin disclosed a quick change system for mold bases employing adapter frames which are attached to the platens of the molding machine. Such quick change system allows mold bases, equipped with standard ear plates, to be changed in a press in ten minutes, or even less time.
U.S. Pat. No. 4,929,170 to Boskovic discloses an ejector blade for ejecting parts from injection molds after a part has been formed, but does not mention adjustability.
Ejector pins are common parts of plastic injection molds. Pins of various sizes and shapes are used to help remove parts from a mold as the mold cavity is opened. Typical ejection pins are illustrated in U.S. Pat. Nos. 3,794,287, 3,852,011; 3,900,183, and 4,162,138.
While ejector pins, whether round, flat or otherwise shaped, are effective in normally ejecting plastic parts from a mold, they do suffer deficiencies. First, because pins are a unitary part, the injection molder must stock a larger quantity of pins of different sizes, lengths, and configurations in order to accommodate different molded parts. Secondly, because pins are single piece structures, they are quite rigid, and any variations in a mold, whether it is due to improper tolerances or unequal expansion of one mold part relative to the other, cannot be accommodated by a pin. Such variations often lead to bending or breaking of the pins, requiring their replacement. Boscovic's patent provided a solution to the above deficiencies in the prior art, and others, by providing an ejector blade for a plastic injection mold which comprises a series of parts, namely an elongate shank portion, a blade portion, and means releasably joining the shank portion to the blade portion at the ends thereof, so that different blade portions can be mounted on a given shank portion. In the preferred embodiment of Boscovic's invention, blades of differing lengths can be secured to one shank, while shanks of differing lengths can be used with a blade of a particular length providing substantial versatility to the ejector blade.
U.S. Pat. No. 3,963,209 to Muller discloses an ejector pin assembly for injection molding tools in which the ejector pin plate of the tool is adapted to be brought back by force to the idle original position thereof in connection with the clamping or closing of the mold.
The primary object of the Muller invention is to provide an ejector pin assembly that guarantees the forced retraction of the ejector pin plate to the original position and at the same time fixedly locks the same in the rear position thereof. This later characteristic is of special importance by the use of high-speed machines where there is a danger that the ejector pin plate is brought to undesired movement by recoil forces or the lie.
The function of the adjustable knockout of this invention in the mold of an injection molding machine is to push the plate injector outward to take out the molded parts and then return the plate injector to its original position. This knockout rod could run different molds because it adjusts to the desired length reducing the setup time, the unnecessary breakage of machines, and reducing by 50% or more the quantity of knockouts used in the area.
No prior art has been found to disclose adjustable knockout or ejector pins or tools for use in injection molding machines.
However, various types of knockout rods or ejector pins are available in the prior art, including one which discloses a “quick adjustment knockout rod”. U.S. Pat. No. 3,448,488 to Kiraly discloses a “quick adjustment knockout rod” but not an adjustable one. The disclosure in Kiraly is directed to quick adjusting knockout rods which have particular utility when used in conjunction with injection molding machines.
While these devices or methods in the prior art fulfill their respective, particular objectives and requirements, none of them disclose an adjustable knockout or ejector pins or tools for use in injection molding machines. Thus, it can be appreciated that there is a continuing need for an adjustable knockout for use in injection molding machines which overcomes these and other deficiencies in the prior art.
In this respect, the adjustable knockout according to the present invention substantially departs from the conventional concepts and designs of the prior art and, in doing so, provides an adjustable knockout that fulfills the aforementioned need.